This invention pertains generally to vapor deposition of films on substrates and more particularly to a reactor and process suitable for depositing materials such as Si.sub.3 N.sub.4 and SiO.sub.2 on semiconductor wafers.
Heretofore, silicon compounds have been deposited on semiconductor wafers in hot-wall reactors which commonly include an elongated tube defining a reaction chamber and an electrical resistance heater surrounding the tube for heating wafers in the chamber. Reactant gases flow through the chamber in an axial direction, and the wafers are positioned with their major surfaces perpendicular to the direction of gas flow.
With certain reactions, the films deposited in such reactors exhibit substantial nonuniformities both within individual wafers and from wafer to wafer. Such nonuniformities occur, for example, in the following reactions for depositing Si.sub.3 N.sub.4 and SiO.sub.2 : EQU 3SiH.sub.4 +4NH.sub.3 .fwdarw.Si.sub.3 N.sub.4 +12H.sub.2 at 850.degree. C. EQU SiH.sub.4 +20.sub.2 .fwdarw.SiO.sub.2 +2H.sub.2 O at 450.degree. C.
With these reactions and the hot-wall reactors of the prior art, the film deposited on a wafer can be as much as 50-500% thicker toward the edges than toward the center, and the films deposited on downstream wafers can be as much as 3-100% thinner than the films deposited on wafers located closer to the gas source.
There have been attempts to improve the uniformity of the deposited films by adjustment of the spacing between the edges of the wafers and the side wall of the reactor tube and the spacing between adjacent wafers. While such attempts have sometimes resulted in more uniform films on individual wafers, they tend to accentuate the variations from wafer to wafer.